Reconstructing bombs first step in finding bomber, experts say

Explosions leave 'quite a lot of evidence behind,' ex-ATF agent says

Debris scattered along Boylston Street a day after two explosions hit the Boston Marathon could provide clues for law enforcement officials hunting down those responsible. (JESSICA RINALDI, Reuters Photo)

As investigators try to figure out who was behind the Boston Marathon attack, the distinctive characteristics of Monday's bombing as well as the lessons learned from past acts of terrorism should provide valuable clues.

Those clues, such as the use of crude "pressure cooker" bombs, likely won't by themselves identify a suspect in the blasts but will help guide the law enforcement effort in its first days.

"The main thing you focus on at the beginning are the details of the attack and the characteristics of the bombs and the geography of the attack," Robert Pape, a professor at the University of Chicago and director of its Chicago Project on Security and Terrorism, said Tuesday. "This begins to get you inside the mind of the attacker even before you're sure who that attacker is. It's the information you work with when you don't have anything else."

Indeed, Pape and other experts as well as current and former law enforcement officials describe a profiling of sorts that begins in the immediate aftermath of an attack. Much as police examine a crime scene for clues, these profilers study the scenes of terrorist attacks for intelligence.

Investigators, according to the experts, have been sifting through that information to identify which clues to pursue most aggressively.

"The initial stage is figuring what matters and what doesn't and avoiding the temptation to jump to conclusions," said Dwight Holton, the former U.S. attorney in Oregon whose office prosecuted a man convicted in a plot to bomb a Christmas tree lighting ceremony in Portland. "That's incredibly important."

Holton said investigators would focus on physical evidence gathered at the scene, interviews with victims and witnesses, and ample video taken around the finish line of the annual race — the traditional methods for any investigation in this high-tech terrorism age. They will also no doubt track cellphone traffic and probe informants for leads on potential suspects.

Mark Jones, a retired agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives who specialized in explosive devices, said investigators were profiling not only the bomber but also the bomb itself. The investigators, he said, would examine the perimeter of the blasts to collect even the tiniest pieces of the explosives.

Residue, for instance, would be analyzed for hints as to how it was detonated. Components will be traced to their manufacturers if possible and from there to whoever obtained them by using any markings on them, records of purchase and their chemical composition, a number of experts said. Authorities would attempt to reconstruct the devices and then run them through a national database on explosions and arsons across the country to possibly point investigators to similarities from the past.

"An explosion does not destroy all the evidence but in fact leaves quite a lot of evidence behind," said Jones, who worked at ATF for 20 years.

While detonating the bombs in quick succession suggested a somewhat complex effort, experts said, the use of just two devices, particularly made from crude materials such as powder, nails and ball bearings, was a sign it likely was not the work of the most sophisticated terrorists — though they did not rule that possibility out either.

Add to that the fact that the bombs seemed designed not so much to kill as to injure and maim, and a portrait begins to emerge of a perpetrator perhaps trying to make some kind of statement rather than cause a large number of deaths, the experts said.

Pape, whose project at the University of Chicago has studied every suicide bombing over the past decade as well as numerous other terrorist attacks, said al-Qaida conducts mostly suicide attacks and is quick to claim responsibility for them — even to boast about them. In this case, at least one al-Qaida group has denied responsibility.

"It's not to say that it's definitely not al-Qaida here," Pape said. "But this is a pattern that doesn't fit al-Qaida's pattern for the last 15 years."

Instead, the Boston attack could fit a rising pattern of disturbing, violent domestic attacks. Karen Greenberg, who runs Fordham University's Center on National Security, said those include the Colorado theater shootings last July and the recent shootings of two Texas prosecutors.

Yet it's simply too soon to assess whether Monday's attack might be the work of international or domestic terrorists or something else, she noted.

"There are pieces of this that could look like international. There are pieces that could look domestic," Greenberg said. "There are pieces that could look like a lone person."

Holton, the former Oregon federal prosecutor, said the availability of bomb-making materials means law enforcement officials in Boston must cast a wide net for potential suspects, including those with no ties to terrorist organizations.

"Sometimes people who are simply deranged use bombs," he said. "That's something you can't rule out."

John Diwik, a former FBI agent, also cautioned restraint, even though he thinks it's "an extraordinary coincidence" that the attack took place on Patriots Day.

"(There's) an awful lot of unanswered questions," said Diwik, who retired after 24 years with the FBI. "Logic would suggest a lot of things. We're going to have to wait for science and technology to prove it."